A conventional process for removing fine particles, organic matter, metal, and other substances from a surface of electronic materials such as silicon wafers for semiconductors, glass substrates for flat panel displays, and quartz substrates for photomasks is the so-called RCA cleaning process, which is a high-temperature wet cleaning process that uses concentrated chemical agent solutions including mainly hydrogen peroxide. The RCA cleaning process is effective for removing metal and other substances on a surface of an electronic material. As the RCA cleaning process uses a large amount of treating liquid containing acid, alkali, or hydrogen peroxide at a high concentration, waste water discharged from the process contains them. Such waste water is required to be treated by neutralization, segmentation or the like which needs a high cost and produces a large amount of sludge.
Gas-dissolved water prepared by dissolving a gas in pure water and optionally adding a slight amount of a chemical agent, has come to be used instead of the above treating liquid. Cleaning with gas-dissolved water is less problematic in terms of chemical agent residues left on the cleaned subject, and also has high cleaning effect and thus reduces the amount of water used for cleaning.
The gases that are used for gas-dissolved water to be used as cleaning water for electronic materials include hydrogen gas, oxygen gas, ozone gas, rare gas, carbon dioxide gas, and so forth.
Known cleaning methods include high-pressure jet cleaning, in which a cleaning liquid is jetted from a nozzle at a high pressure, two-fluid cleaning, in which a cleaning liquid and a gas (carrier gas) are jetted from a two-fluid nozzle, and so forth. A high-pressure jet cleaning process or a two-fluid cleaning process produces a satisfactory cleaning effect due to physical action of droplets of the cleaning liquid jetted from the nozzle and colliding with the subject at a high speed.
The cleaning effect of gas-dissolved water is admittedly higher than the cleaning effect of water containing no dissolved gases, but fine particles are not fully removed by a high with high-pressure jet cleaning process or a two-fluid cleaning process alone. These cleaning processes obtain high cleaning effect in combination with ultrasonic cleaning. Patent Document 1 proposes a cleaning method containing a process for preparing a cleaning liquid by dissolving hydrogen gas in ultrapure water and adding hydrogen peroxide, and a process for cleaning a subject with the cleaning liquid while irradiating ultrasonic to the cleaning liquid.
However, an ultrasonic cleaning equipment is expensive and thus causes an increased cleaning cost. Furthermore, cleaning glass substrates or the like with gas-dissolved water and ultrasonic requires a large amount of cleaning water, since ultrasonic is irradiated to the substrate using a squall nozzle or the like.
If a sufficient cleaning effect is achieved with a high-pressure jet cleaning process or a two-fluid cleaning process, above-described problems in the ultrasonic cleaning process is solved, and resource-saving cleaning method will be conducted at a low cost. However, the high-pressure jet cleaning process or the two-fluid cleaning process with gas-dissolved water can not achieve a sufficient cleaning effect.
Patent Document 1: Japanese Patent Publication 2004-296463A